Cancer patients who have been treated by radiation therapy to the mediastinal (including thymus) or pelvic area will be studied during radiation therapy and recovery from radiation therapy. The studies will include evaluation of the blood lymphocytes to enumerate and classify them as thymus-derived or bone marrow derived (potential antibody- forming) cells by the use of rosette and immunofluorescence techniques. The function of these cells will be also evaluated in vitro by their ability to divide and to produce an effector substance or a lymphokine (lymphotoxin) after exposure to various mitogenic substances which are thought to stimulate only certain lymphocyte subpopulations. The patterns of change during and after radiation therapy will be examined to determine whether they provide a clue to the prognosis of the patients. In addition, the patterns of change will be compared in the two groups--mediastinal and pelvic radiation--to determine whether irradiation of the thymus may cause a long-term suppression of cellmediated immunity.